The present invention relates to a helicopter rotor. In particular, the present invention relates to an articulated rotor on which each blade is connected to the center hub on the rotor by means of a fork, in turn, connected in articlated manner to the said hub.
On articulated rotors of the aforementioned type, each blade oscillates, in relation to the hub and about the said articulated joint, both vertically in a plane perpendicular to that of the hub, due to lift, and horizontally in the hub plane, due to inertia and drag.
Known rotors of the aforementioned type usually present limiting devices for maintaining vertical and horizontal oscillation within relatively limited angles, below a given rotor speed.
In particular, the said limiting devices are known to comprise rocker arms mounted on the said fork or hub and designed to move, by virtue of centrifugal force, between a normal idle position, wherein the said rocker arms cooperate with contact surfaces on the said hub or fork, for limiting the said oscillation, and a working position wherein the blade is free to oscillate.
The main drawback of articulated rotors featuring limiting devices of the aforementioned type is that the said articulated joint connecting the fork and hub allows the blade, not only to oscillate vertically and horizontally, but also to perform a pitch-change rotation about its own axis, which obviously results in displacement of the said contact surfaces and the paths of the respective rocker arms. The effect of such displacement is to impair contact between the said rocker arms and respective contact surfaces, which inevitably increases wear and impairs the efficiency of the said limiting devices.
This is extremely dangerous as far as vertical oscillation control is concerned, in that, whereas horizontal oscillation is kept under control by means of hydraulic dampers between the blade and hub, low-speed vertical oscillation is generally controlled solely by the said rocker arms. Consequently, any impairment in the efficiency of the said rocker arms may, especially during take-off, and due to both wind and the well known "ground effect", result in sharp pitching of the blades and overturning of the helicopter.